High-Power CO2 Laser System with Repetition Rate Operation for High Current Multicharged Heavy Ion Generations

Experimental and numerical calculation results devoted to development of an optical system for an ion source based on a repetition rate CO₂ laser are described. The laser chain consists of a master oscillator, gas absorber cells, and a four-pass amplifier. The optical system provides smooth laser pulses with variable duration and high spatial quality that ensures efficiency for plasma heating and ion generation. The parameters of the plasma ion component measured in the CERN laboratory are applied for a lead target illumination.     

一种微型空调器的优化设计

介绍了一种微型空调器的研制背景及设计方案 ,采用仿真优化的设计手段对空调器的制冷、制热系统进行了优化设计 ,实践证明其设计是成功的。同时说明了该型空调器所具有的特点及应用场合     

三维层流等离子体射流中陶瓷颗粒的运动与加热

本文对带载气-颗粒侧向喷射的三维层流等离子体长射流中陶瓷颗粒的运动与加热进行了模拟研究,并与忽略载气喷射影响时的结果进行了比较。模拟结果表明,侧向载气喷射所引起的三维效应对颗粒行为有明显影响,陶瓷颗粒在等离子体射流中加热时颗粒内部可能出现相当大的温差,取决于环境参数,陶瓷颗粒表面温度可以高于也可以低于中心温度。     

翼前缘层板对流冷却结构的防热效果分析

针对飞行器高超声速飞行时严重的气动加热环境, 设计一种层板对流冷却结构对翼前缘进行热防护. 提出一种壁面冷却效率参数η, 并运用流固耦合的分析方法, 研究了对流冷却结构在特定条件下的冷却效果, 其中采用水冷时头部冷却效率η 值最低为0.25. 研究表明, 对流结构冷却效果与内部冷却槽道深宽比γ 有重要关系, η值随γ 的增大而增大至一个稳定值, 此时冷却效果达到饱和, 若此时γ 继续增加则可能出现不利于冷却的现象. 冷却效果η随着前缘头部半径的减小而减弱. 研究还表明, 当层板对流冷却结构和材料固定时, η 值随冷却剂流量增加而增大, 并逐渐趋近至一个稳定值, 而冷却槽道进出口压差急剧增大. 因此需要综合考虑提高流量给供给系统带来的压力, 选取最佳流量值以达到相对较好的冷却效果. 对于材料而言, 内部冷却通道和外部耐热层都应选择导热系数较高的材料, 能够强化结构传热增强冷却效果.     

Electric current control of creation and annihilation of sub-100 nm magnetic bubbles examined by full-field transmission soft X-ray microscopy

The effect of electric current pulses on a sub-100 nm magnetic bubble state in a symmetric Pt/Co multilayer was directly observed using a full-field transmission soft X-ray microscope (MTXM). Field-induced evolution of the magnetic stripe domains into isolated bubbles with their sizes down to 100 nm was imaged under varying external magnetic fields. Electric current pulses were then applied to the created magnetic bubbles, and it was observed that the bubbles could be either created or annihilated by the current pulse depending on the strength of applied magnetic field. The results suggest that the Joule heating plays a critical role in the formation and/or elimination of the bubbles and skyrmions. Finally, the schematic phase diagram for the creation and annihilation of bubbles is presented, suggesting an optimized scheme with the combination of magnetic field and electric current necessary to utilize skyrmions in the practical devices.     

Transverse Transport of Polymeric Nanofluid under Pure Internal Heating: Keller Box Algorithm

The present work aims to investigate transverse Oldroyd-B nanofluid flow on a stretched panel with consideration of internal heat generation. Buongiorno model is utilized to study influence of thermophoresis and Brownian motion effects. A numerical procedure known as Keller box algorithm is used to solve the governed physical model. Graphically velocity, temperature and concentration of nanoparticles are expressed. Also, concerned physical measures such as heat and mass transfer are investigated numerically. The simulations performed revealed that fluid parameters play a significant role in heat transfer under Brownian motion and thermophoresis effects. Local heat flux is elevated while local mass flux is suppressed with enhancing Brownian motion parameter. Streamlines pattern exhibits that flow is more inclined in the presence of Deborah number effects. To the best of our knowledge, transverse flow of an Oldroyd-B type fluid which incorporates the thermal relaxation effects has never been reported before in the presence of Brownian motion and internal heating phenomenon. Therefore we intend to discuss these features in detail. The obtained results are a novel contribution, which can be benchmark for further relevant academic research related to polymer industry.     

Laser pulse heating: Cavity formation into steel, nickel and tantalum surfaces

The cavity formation during laser pulse heating of steel, nickel, and tantalum is examined and evaporation rate from the cavity surface is predicted. The mushy zones generated across the vapor–liquid and liquid–solid phases are modeled using the energy method. Temperature-dependent thermal properties are accommodated in the analysis and the laser pulse shape resembling the actual laser pulse is employed in the simulations. A numerical scheme using the control volume method is used to predict the cavity size, recession velocity of the vapor front, and temperature field in the laser irradiated region. It is found that cavity depth for steel is the largest, then follows nickel and tantalum. The recession velocity of the vapor front is high for steel due to the low evaporation temperature and latent heat of evaporation of steel.     

Tip‐heating‐assisted Raman spectroscopy at elevated temperatures

We demonstrate tip‐heating‐assisted enhanced Raman spectroscopy to investigate the temperature dependence of the carbon nanotube G‐band with nanoscale resolution. The controllable and nanoscale heat generated at the tip apex was used to thermally perturb and characterize a small volume in a carbon nanotube sample that is precisely positioned underneath the tip. The dependence of tip enhancement with temperature was also experimentally examined, which is in good agreement with the enhancement calculated from the electromagnetic model of isolated spheroids. The technique presented may open up opportunities in the study of controlled heat‐assisted biochemical reactions and physical transformations of nanostructures. It can also be used for thermal characterization of various materials requiring site‐selective and controllable nanoscale heat source and could enable the realization of new photothermal devices. Copyright © 2010 John Wiley & Sons, Ltd.     

Excimer laser accelerated hydrothermal synthesis of ZnO nanocrystals & their electrical properties

The synthesis of ZnO nanocrystals is reported using a hydrothermal chemical growth technique combined with 248 nm nanosecond excimer laser heating at fluences in the range 0-390 mJ cm⁻². The effect of laser heating in controlling the morphology of the nanocrystals is investigated using optical spectroscopy and electron microscopy characterization. Laser heating is shown to allow control of the crystal morphology from nanoparticles to nanorods as well as to modify the size distributions. The results indicate that not only does the laser accelerate the growth of nanocrystals, but can also produce crystals with a narrow size distribution possibly via photothermal size selection. An initial study of electrical conduction properties of ZnO nanocrystal thin films is also discussed.     

金刚石/ZnSe结构中瞬态热栅场的有限元法分析

利用有限元法分析计算了脉冲激光激发瞬态热栅在金刚石薄膜/ZnSe衬底双层结构中的三维温度场分布及变化。通过比较不同厚度金刚石薄膜样品的温度场分布,结果显示金刚石薄膜的厚度对样品中温度场的分布有较大影响,随着薄膜厚度的增大,峰值温度提高并且二次加热现象更加明显。